Multiple driver dynamic loud speaker

ABSTRACT

A loud speaker assembly capable of producing coherent sound with multiple driver, dynamic loud speakers is provided, which assembly is characterized by sonic frequencies of the mid-range and treble frequency bands being generated by wide dispersion, dynamic transducers which are free-air mounted within an accoustically transparent enclosure. The mounting of all of the transducers in the assembly is preferably coordinated as a function of the rise time characteristics of the transducers by positioning the transducers forwardly and rearwardly in the assembly along their radiating axes with respect to a listening area, in such manner that the sound waves generated by electrical signals simultaneously impressed upon the transducers will be simultaneously impinged upon a point in the listening area equidistant from the radiating axes of the transducers.

United States Patent 1191 Dahlquist 1451 July 16, 1974 1 1 MULTIPLEDRIVER DYNAMIC LOUD SPEAKER [76] Inventor: Joh G. Dahlquist, 500 E. 85thSt.,

New York, N.Y. 10028 22 Filed: Nov. 29, 1972 21 Appl. No.2 310,535

52 us. (:1 179/1 E, 181/31 B 51 ,Int. Cl. ..Gl0k11/00 [58] Field ofSearch... 179/1 E, 1 D; 131/31 B [56] References Cited i UNITED'STATESPATENTS 2,217,279 10/1940 Karns 181/31 B 3,105,569 10/1963 Evans 181/31B 3,385,929 5/l968 Magyar et a1 181/31 B 3,666,041 5/1972 Engelhardt181/31 B FOREIGN PATENTS OR APPLICATIONS 1,216,851 5/1963 France 181/31B 1,339,664 9/1963 France 181/31 B 1,042,024 6/1956 Germany", 179/115Primary E.ran1iner-Kathleen H. Claffy Assistant ExaminerDouglas W. OlmsAttorney, Agent, or Firm-MaikT. Basseches; Paula T. Basseches [5 7ABSTRACT A loud speaker assembly capable of producing coherent soundwith multiple driver, dynamic loud speakers is provided, which assemblyis characterized by sonic frequencies of themid-range and treblefrequency bands being generated by wide dispersion, dynamic transducerswhich are free-air mounted within an accoustically transparentenclosure. The mounting of all of the transducers in the assembly ispreferably coordinated as a function of the rise time characteristics ofthe transducers by positioning the transducers forwardly and rearwardlyin the assembly along their radiating axes with respect to a listeningarea, in such manner that the sound waves generated by electricalsignals simultaneously impressed upon the transducers will besimultaneously impinged upon a point in the listening area equidistantfrom the radiating axes of the transducers.

5 Claims, 6 Drawing Figures MULTIPLE DRIVER DYNAMIC LOUD SPEAKERBACKGROUND or THE INVENTION 1. Field of the Invention The presentinvention is in the field of high fidelity sound reproduction andrelates more particularly to a high fidelity loud speaker assembly ofthe multiple driver, wide dispersion dynamic type.

2. The Prior Art It is known to provide as a means for reproducing soundan assembly comprising two or more transducers of the so-called dynamicor permanent magnet type, each of which transducers is connected to afrequency dividing network or crossover which functions to divide thefrequencies of the output of an audioamplifier into frequency bands, andto apply the bands thus obtained to the respective transducersespecially constructed or adapted to reproduce such bands.

Typically, speaker assemblies of such known types incorporate anenclosure or chamber with or without venting means, the front face ofthe enclosure being defined by a baffle or board to which thetransducers are mechanically connected, the baffle being provided withapertures through which sound may be radiated.

As conducive to an understanding of the present invention, it should beexplained that the typical multiple transducer loud speaker assemblyemploying wide dispersion transducers,'i.e., cone or dome type speakers(but not horn type speakers) wherein the diaphragms are directly coupledto the air load, incorporate a direct connection between the drivers andthe front board, wall or baffle of the box, enclosure or chamber.

Typically the transducers include a perimetal ring or rimprovided withmounting holes bolted to the inner or outer face of the baffle. Thewoofer or bass reproducer may be housed within a separate enclosure, the

front wall of which is defined by the front baffle, or separatesub-enclosures may be formed, each of which sub-enclosures nonethelessemploys a front baffle member.

Substantial activity has been undertaken in the field of improvingspeaker systems of the type described, all of which systems suffer, ingreater or lesser degree, from a lack of coherence, as hereinafterdefined. The avenues of investigation heretofore attempted have includedthe utilization of various porting devices, air

coupling schemes, means for damping or controlling spurious vibrationsof the diaphragms and enclosures, etc. Notwithstanding the improvementsin enclosure design and in transducer design, units heretofore knownhave all suffered from a common boxiness or constriction of sound,readily identified by expert listeners.

While there are in existence electrostatic loud speakers which arecapable of producing more or less coherent sound, free from theunpleasant distortions above set forth, electrostatic speakers ofnecessity incorporate certain drawbacks which detract from theirwidespread use, i.e., high initial expense, large overall size,fragility, the necessity for providing a well regulated high voltage DCpower supply, required proximity to an electrical outlet, etc.

l have discovered that many of 'the deficiencies in prior art speakersystems are not due to deficiencies in the transducers themselves but,rather, are due to the manner in which the speakers have been mounted. l

2 have discovered that lack of coherence of sound in such systems is, inlarge measure, attributable to what will be termed baffle propagationeffects.

By way of explanation of the term baffle propagation effects, if amoving coil loud speaker or wide dispersion transducer were held in freeair, e.g., a 1 inch dome driver radiating a 1000 Hz tone, it will benoted that the tone is audible whether or not the dome or diaphragmdriver is facing a listener. The driver may be said to have anomni-directional radiation characteris tic at such frequency. If,however, the same driver is now mounted on a baffle or surface which isrelatively rigid and substantially larger than the speaker diaphragmitself (the baffling system universally used at the present time), theradiation which was free to propagate behind the transducer is nowconstrained to the frontal hemisphere over the larger area defined bythe baffle. I

l have discovered that the thus baffled transducer results in theproduction of a high intensity sound field which propagates outwardly inall directions along the surface of the baffle until it encounters adiscontinuity, such as a raised portion or an edge or a terminus of thebaffle.

I have further determined that a diffraction occurs at suchdiscontinuity, edge or terminus, which diffraction results in theproduction of. secondary virtual sound sources at the discontinuity,edge or terminus, which secondary sourcesinescapably introduce into theaudible signal time delay distortion products. Obviously, the sounddirectlyradiated by the diaphragm and that radiated by secondarysources, by reason of the displacement of the secondary sources from thediaphragm, will inherently be carried to the ear of the listener atdisplaced time intervals, a factor which, in large measure, accounts forthe lack of coherence in the conventional baffle mounted speaker system.

The so-called baffle propagation effects induce additional distortionproducts in the audible signal, which reduce the naturalness of thereproduced sound. Specifically, the secondary radiating sources havebeen found to be frequency dependent, i.e. the secondary radiatingsources may emphasize one frequency over another. Thus, if a bafflemounted transducer is emitting a blend of frequencies of, for example,4000 Hz and 6000'Hz, of equal intensity, the propagating'characteristicsof the baffle board and secondary sources may be such as to disseminatethe 4000 Hz tone with greater efficiency than the 6000, with the resultthat the musical balance will be altered.

Still another difficulty inhering in baffle board propagation is thefact that the high intensity energy propagated by one transducer alongthe baffle surface is impinged upon the cone and voice coil structure ofall of the other transducers mounted on the same baffle, resulting inthe production of intermodulation distortion products and microphonics,since vibrations applied to the diaphragm must also affect the movementof the voice coil.

1 have discovered that by eliminating the baffle of the speakers,particularly the speakers other than the bass reproducer, namely, thosereproducing above about 400 to 500 Hz or higher, the sound reproductioncharacteristics of the multi-speaker, wide dispersion assembly isdramatically improved;

I have further discovered that the elimination of time delay distortioneffects introduced by baffle mounting of the mid and high frequencyreproducers, particularly SUMMARY OF THE INVENTION The present inventionmay be summarized as relating to a coherent sound source incorporatingmultiple wide dispersion drivers of the dynamic type, the drivers beingof the wide dispersion type (as opposed to incorporating a horn type,air coupling system). The assembly includes a more or lessconventionalwoofer or bass transducer, which is preferably mounted within a separate enclosure forming a part of the assembly. Positioned within theassembly, but externally of the enclosure, is at least one additionalwide dispersion, dynamic transducer.

It is a characterizing feature of the present invention that said atleast one additional transducer be substantially completely surroundedby free space. Preferably the radiating diaphragm components of the bassradiator and free-space mounted transducer are, in addition, offset onefrom the other in the direction of the listening axis in such mannerthat, notwithstanding any differences in rise time between thetransducers, an electrical signal impressed simultaneously on bothtransducers will result in the production of a sound impulse which willsimultaneously reach the ear of the listener.

Accordingly, it is an object of the present invention to provideanimproved multiple transducer dynamic speaker'assembly.

It is a further object of the present invention to provide a speakerassembly of the type described which is capable of providing a coherentsound source.

Still a further object of the present invention is the provision of amultiple transducer loud speaker assembly of the type described,employing wide dispersion transducer components and capable ofrecreating sound with a fidelity, clarity and freedom fromaberrations'superior to dynamic speaker assemblies heretofore known;

It is still a further object of the invention to provide an improvedspeaker assembly of the type described which is susceptible of producinga more precise imaging effect than speakers of conventional design.

Still a further object of the invention is the provision of a speakerassembly of the type described which is ca- 4. ence is made. to theaccompanyingdrawings, forming a part hereof, in which:

FIG. 1 is a schematic view of the sound radiation pattern of aconventional baffle mounted, permanent magnet speaker of the dome type;I

FIG. 2 is a perspective view of a loud speaker. assembly in accordancewith the invention, with parts of the clude the following definitions:

Transducer or direct radiating dynamic transducer within the context ofthe instant application is intended to refer to a diaphragm, cone ordome type permanent magnet speaker, as distinguished from anelectrostatic speaker or'a hornloaded driver.

Coherent sound refers to an audible signal containing complexinformation bits, wherein the information bits falling upon the ear ofthe listener arrive in the same temporal relation as the electricalenergy inputs to the loud speaker assembly, i.e., are largely freeofdistortion products and particularly of time delay distortion products.I

Time delay distortion in a loud speaker refers to the distortion of acomplex, (i.e., non-sinusoidal) wave form resulting from lack ofsynchronism. amongthe energy outputs of the various drivers in afrequency divided speaker system. While the total energy output in atime delay distorted signal may be identical with that of an undistortedsignal, the wave forms generated in the distorted signal will differfrom those of the original signal. While some time delay distortioninheres in the energy output of even .a single, unbaffle'd transducer,such distortion products are relatively small at the center of the bandcovered by the speaker but increase toward the upper and lower limits ofthe band.

Rise time" as used herein should be understood to relate to the time laginherent in all transducers between the impressing of a voltage on thetransducer and the diaphragm of that transducer responding to thevoltage. l

Referring now to the drawings, in FIG. 1 there is shown a baffle board Bhaving mounted in a suitable aperture 10 a conventional transducer 11,in this instance a dome type reproducer. It will be appreciated that, asis typical, the Board B may form the front face of a loud speakerenclosure, the side walls W and W" of which are shown.

As is thecase with all of the transducers hereinafter referred to, andas is well known, the-radiating diaphragm, dome or cone D of thetransducer 11 is mechanically connected to a voice coil comprising oneor more turns of a conductor. mounted within a high inten-.

' sity magnetic field. The diaphragmand-coil are sup ported forreciprocal movement in a directiongenerally paralleling the listeningaxis L-L. When an audio signal is impressed upon the voice coil, thediaphragm will be caused to move, generating sonic energy radiated inpattern P. i

[have discovered that by baffling the transducer ll in the manner noted,substantial amounts of sonic energy,-viz. the energy generated at thefront of the speaker which would, in the absence of baffling, beradiated rearwardly, are propagated along the surface S of the baffle B,in patterns of propagation schematically represented by the wave frontsl2 and 13. When the high concentration of sonic energy reaches the edges14 and of the baffle or at any discontinuity or abutment on the baffleface, there are created secondary radiating sources, such as P and P",which radiating sources will provide secondary propagation pointsorareas radiating sound waves.

As previously noted, the wave fronts produced by the secondary soundsources P and P" are, of necessity, out of timed sequence with the soundproduced by the principal source P by a temporal delay factor which afunction of the time required for the high energy sound to travel fromthe transducer 11' to the edges 14 and 15. While the intensity of thefields P and P" is substantially less than the intensity of theprincipal radiation pattern P, they will nonethelessintroducesubstantial timewdelay distortion products in the audiblesignal, which distortion products will necessarily detract from therealism of the musical or other sounds generated. Since thesecondarysources P, P" radiate different frequencies with varyingefficiencies, the tonal balance of the radiations from points P and P"may differ significantly from that of the primary source, furtherdegrading the accuracy and acoustical frequency balance of the soundwaves. Further, secondary radiating sources have unpredictable polardistribution patterns which are likewise frequency dependent.

- The existence of the secondary or virtual radiating points P and P"will necessarily reduce the imaging ability of a stereo or quadrophonicsystem since spurious information is emanating from positions displacedfrom the actual sound source. As a result, whereas in' an ideal stereosystem a listener is able to locate or imagine the virtual location of agiven instrument in an overall pattern of sound, and such abilityprovides a substantial degree of satisfaction and realism, the existenceof secondary radiating areas will introduce errors in perspective.Manifestly, the secondary. or virtual sound sources will interfere withthe imaging characteristics of the speakers, i.e., the ability of thespeakers accurately to recreate the proper spacial location of thecomponents of the audible signal.

A further problem inhering in the baffle mounting of speakers istheresultant reduction of the dispersion of the speakers and theintroduction of polar lobe patterns.

A further distorting influence in multiple speaker systems employingbaffles, the means conventionally employed for mounting the transducers,is the fact that frequently the woofer, mid-range and tweeterreproducers are mountedwith their diaphragms in coplanar alignment or,worse, with the diaphragms of the midrange and tweeter advanced in aplane closer to the listener than the diaphragm of the woofer.

Since the rise time of a permanent magnet speaker unit is a functionlargely of the mass and area of the diaphragm and voice coil assemblyand the strength of the magnetic field. the rise time of a woofer, withits larger and heavier diaphragm, is nearly always greater-than that ofthe mid-range reproducer which, for the same reasons, is typicallygreater than that of the tweeter or Y 6 1 high frequency reproducer. Itwill be appreciated that coplanar baffle mounting of' woofer, mid-rangeand tweeter introduces additional aberrations into the audible signal inthat the transducer capable of responding most rapidly to an electricalaudio signal is also disposed most closely to the ear of the listener.As a result, electrical signals in different frequency bandssimultaneously impressed on different transducers and which are intendedto reach the ear of a listener at a given instant of time, will bereceived at different instants of time, which different instants will beseparated not only by the inherent rise time differences of thetransducers but, in addition, by the fact that the tweeter may bemounted forwardly and, hence, more closely to the ear of the listenerthan the diaphragm of the woofer.

The reproduction of a complex acoustical wave form, such as a pulse,square wave, requires that the low frequency and high frequency signalcomponents be superimposed with specified amplitude in the specifiedtime sequence. Otherwise, in the absence'of synchromization, a wave formwill be produced which has the same frequency spectrum as the originalsignal but different wave shape.

There is shown in F IG. 2 a loud speaker assembly 15 in accordance withthe invention. The assembly 15 includes a woofer enclosure portion 16 ofconventional design, and maybe of the bass reflex, infinite baffle, airsuspension or, preferably, so-called transmission line type.

The woofer enclosure includes a base or bottom wall 17, side walls 18,19, rearwardly angled back wall portions 20, 21, a rear wall 22 and atop wall 23. It will be appreciated that the shape of the wooferenclosure 16 is not critical. A woofer member 24 is mounted in standardfashion to the front wall 25 of the woofer enclosure.

The speaker assembly includes a plurality of additional transducers 26,27, 28, 29, respectively for reproducing mid-range, upper mid-range,high frequency and ultra high frequency bands. It will be appreciatedthat four additional transducers need not be employed, theme of twonormally being adequate for full coverage of the audible spectrum.

As is conventional, a frequency divider network 30 is provided,functioning in the usual fashion to divide the input signals intovarious band widths, the outputs of the frequency divider network 30being led to the appropriate transducers 24, 26, 27, 28, 29 designed toreproduce such band width.

Critical to the improved operation of the instant system is the free-airmounting of the transducers 26 to 29. The term free space mounting isintended to connote a condition in which the transducers 26 to 29 arestructurally supported to the loud speaker assembly with the supportmeans incorporating a minimum of area, and particularly of area facingin the direction of the listener. Obviously, in order to secure thetransducers 26 to 29 at a predetermined location within the speakerassembly, some physical support is necessary. Hence the term free spacemounted describes an ideal but theoretical condition.

In the embodiment of FIG. 2, the transducers 26 to 29 are supported uponstruts 26', 27', 28' and 29', respectively, which struts present, in thedirection of the listening axis, a minimum of surface area.

Optionally and preferably, the side faces of the struts 26' to 29 andthe outer surface of the top wall 23 of the woofer enclosure are paddedwith sound absorptive materials to minimize reflection.

For appearance purposes, the speaker assembly is provided with anacoustically transparent frame 31 extending along the sides 18, 19 ofthe woofer enclosure and a distance thereabove, the frame including atop stretcher member 32. An acoustically transparent but opticallyopaque grille cloth 33 is stretched over the entire front face ofthe'assembly and over at least the rear face portions of the assemblyabove the woofer enclosure.

The areas within the frame but external of the woofer enclosure arepreferably free from sound reflecting surfaces and, accordingly, if theframe components are formed of solid materials, such as wood or thelike, the portions of such frame components are preferably covered withsound absorbing materials.

It is desirable that no substantial reflecting surfaces be presentwithin the portions of the assembly within the frame but external of thewoofer enclosure.

Optionally, the speaker assembly may be provided with an acousticallysemi-transparent blanket to be disposed rearwardly of the transducers inorder that backward radiation from the speakers26 to 29 is somewhatreduced, so that if the speaker assembly is placed adjacent or inproximate relation to a wall in the listening room, rearward radiationwill be reduced as compared to forward radiation.

As best appreciated froman inspection of FIGS. 3 and .4, the positionsof the speakers are offset from one another in the direction of thelistening axis, with the woofer 24 being disposed forwardly of themid-range speaker 26, which is in turn disposed forwardly as respectsupper-mid-range driver 27, which is in turn disposed .forwardly'oftweeter 28, which is in turn disposed forwardly of super tweeter 29.

The condition thus schematically illustrated is intended to show themanner of disposing the transducers in accordance with their rise timecharacteristics. While the illustrations herein are intended to beschematic only, it should be appreciated that the spacing X (FIG. 3)between the major radiating surface of the scope. The higher frequencytransducer is then adjusted forwardly or rearwardly relative to the topwall portion 23 until the square wave form picked up at a microphoneequidistant from the speaker axes and observed on the oscilloscope is asnear perfect as possible.

Once the position of the transducers is established, for instancetransducer 26 relative to the woofer 24, the process is repeated, usinga square wave covered by transducers 26 and 27, to establish'the properpositioning of the transducer 27. The process is repeated to establishthe correct positioning of the remaining transducers.

Normally, in production, the transducer units will be sufficientlyconstant in their rise time characteristics to permit the establishmentof a'selected spacing, without requiring individual testing of each unitalthough individual testing is desirable for optimum performance.

In the square wave testing procedures, it is desirable to pass thesquare wave signal through the frequency dividing network sinceconventional networks may, to a degree, introduce time lag and phaseshift effects. It is recognized that the forward and rearward placementof transducers within the enclosure is effective principally in on-axislistening and that listening at a position remote from the axes of thetransducers may involve the introduction ofrise time errors, due togreater proximity to one than to the other of the transducers. Nodesign, however, can completely compenmid-range transducer 26 and thewoofer 24 is calculated as a function of the rise time characteristicsof the respective transducers, such as to handicap the woofer, in thisinstance, with its slower rise time in such manner that-a signalsimultaneously impressed on the terminals of the woofer 24 and mid-rangetransducer 26 will reach the ear of a listener essentiallysimultaneously.

In similar fashion, transducer 27, having a more rapid rise time thantransducer 26, is displaced rearwardly of the transducer 26 a distance Xtransducer 28 rearwardly of transducer 27 a distance X, and transducer29 rearwardly of transducer 28 a distance X"", such that each of thetransducers is appropriately handicapped in accordance with its risetime characteristics.

- It will be understood that the rise time characteristics of thetransducers and, accordingly, their forward and rearward positioningwithin the assembly, may be calculated or experimentally determined inknown manner. However, a convenient empirical manner of positioning thetransducers involves-feeding to a pair of transducers intended to coveradjacent frequency bands, a square wave which spans the frequency bands,and observing the reproduced sound on an oscillosate for rise timechanges, it. being the intention'of the described forward and rearwardorientation to optimize on-axis listening.

- Three or more decorative leg members 34 are preferably fixed to theunder surface of the speaker assembly 15. I

In the embodiment of FIGS. 5 and 6, wherein like parts have been givenlike numbers, it will be observed that the woofer 24 is, in thisinstance, mounted within a generally rectangular enclosure, to theuppersurface 40 of which there has been affixed a tree-like transducersupport 41.

The transducer support 41 is notchedto define recessed transducerreceiver faces42, 43 and 44, for receiving the midrange, tweeter andsuper tweeter transducers 26, 28 and 29, respectively.

It will be appreciated that in this embodiment the forward and rearwardpositioning of the transducers is preset in the fabrication of the tree41, in accordance with the rise time characteristics of the transducers.

As with the prior described embodiment, the area 45 designates anacoustically transparent frame, dome or envelope above the wooferenclosure, the acoustical transparency being present in the. front,sides, top, and preferably, at least to a limited degree, the rearsurfaces of the dome or frame. Additionally, solid surfaces within thedome or frame, such as the upper face of the upper wall 40 of the wooferenclosure and the edges of the strut support 41, are provided with acovering of acoustically absorbent material.

From the foregoing it will be observed that there is provided inaccordance with the present invention, a multiple transducer loudspeaker assembly wherein several of the major deficiencies observed indynamic loud speakerassemblies heretofore known have been eliminated,

It will be understood that the lower frequency limit selected for thefree-space mounted transducers pro ducing the lowest frequency tones maybe set at any frequency sufficiently high to avoid cancellation effects.Normally the frequency reproduced by a freespace mounted transducershould not bebelow about 400 to 500 Hz.

Listening to the speaker fabricated in accordance with the presentinvention, and particularly an on-axis listening, is characterized by anunusual and unique clarity and definition in the mid, upper mid andtreble ranges particularly, making the speaker reminiscent of the finestelectrostatic loud speakers, without the beaming or directivity inherentin such electrostatic speakers in the higher frequency ranges. The loudspeaker assembly exhibits a freedom from coloration which is readilyapparent when compared to a control speaker assembly consisting of thesame transducers and frequency dividing network mounted on a baffle,whether or not the baffle forms a part of an enclosure.

Numerous variations in constructional details may readily suggestthemselves to skilled workers in'the art in the light of the instantdisclosure. Accordingly, the invention is not to be construed as limitedto the specific embodiments illustrated and described herein but,rather, should be broadly construed within the scope of the appendedclaims.

Having thus described the invention and illustrated its use, what isclaimed as new and is desired to be secured by Letters Patent is;

l. A multiple transducer dynamic loudspeaker assembly comprising, incombination, a frame including an acoustically transparent front face,an enclosure within said frame, a bass radiator transducer mountedwithin said enclosure, strut means mounted within said frame andextending externally of said enclosure, said strut means presentingminimal area in the direction of said front face of said frame, at leasttwo additional direct radiator dynamic transducer members positionedwithin said frame externally of said enclosure, said at least twotransducers being supported solely by said strut means and being, withthe exception of the'connection to said strut means, completelysurrounded by I free space, the area within said frame and rearward ofsaid at least two transducers being substantially free of soundreflective surfaces facing the front of said speaker, and a frequencydividing network means for dividing the electrical signals fed to saidloudspeaker assembly into at least three discrete frequency bands, andapplying an appropriate said band to each said transducer.

2. The loudspeaker assembly in accordance with claim 1 wherein portionsof said frame external of said enclosure are substantially acousticallytransparent.

3. The loudspeaker assembly in accordance with claim 2 wherein said rearface of said external frame portion is of lesser acoustic transparencythan said front face.

4. The loudspeaker assembly in accordance with claim 1 wherein theradiating axes of said transducers are substantially parallel and theradiating surfaces of said transducers are displaced one from the otheralong said axes in accordance with the rise time characteristics of saidtransducers a distance whereby the sound wave generated by each of saidtransducers responsive to an electrical signal simultaneously impressedupon said transducers will simultaneously reach a listener in front ofand equi-distant from the axes of said transducers.

5. A loudspeaker assembly in accordance with claim 1 wherein theradiating axes of said transducers are disposed in substantial parallelalignment and are directed toward a listening area forwardly of saidfront face of said assembly, the radiating diaphragms of saidtransducers being displaced one from another in inverse relation to therelative rise time characteristics of the transducers whereby thetransducer having a longer rise time will be disposed closer to saidarea, with the diaphragm of each transducer having a longer rise timethan another transducer closer to a point within said listening areaequi-distant from said diaphragms than having a shorter rise time.

1. A multiple transducer dynamic loudspeaker assembly comprising, incombination, a frame including an acoustically transparent front face,an enclosure within said frame, a bass radiator transducer mountedwithin said enclosure, strut means mounted within said frame andextending externally of said enclosure, said strut means presentingminimal area in the direction of said front face of said frame, at leasttwo additional direct radiator dynamic transducer members positionedwithin said frame externally of said enclosure, said at least twotransducers being supported solely by said strut means and being, withthe exception of the connection to said strut means, completelysurrounded by free space, the area within said frame and rearward ofsaid at least two transducers being substantially free of soundreflective surfaces facing the front of said speaker, and a frequencydividing network means for dividing the electrical signals fed to saidloudspeaker assembly into at least three discrete frequency bands, andapplying an appropriate said band to each said transducer.
 2. Theloudspeaker assembly in accordance with claim 1 wherein portions of saidframe external of said enclosure are substantially acousticallytransparent.
 3. The loudspeaker assembly in accordance with claim 2wherein said rear face of said external frame portion is of lesseracoustic transparency than said front face.
 4. The loudspeaker assemblyin accordance with claim 1 wherein the radiating axes of saidtransducers are substantially parallel and the radiating surfaces ofsaid transducers are displaced one from the other along said axes inaccordance with the rise time characteristics of said transducers adistance whereby the sound wave generated by each of said transducersresponsive to an electrical signal simultaneously impressed upon saidtransducers will simultaneously reach a listener in front of andequI-distant from the axes of said transducers.
 5. A loudspeakerassembly in accordance with claim 1 wherein the radiating axes of saidtransducers are disposed in substantial parallel alignment and aredirected toward a listening area forwardly of said front face of saidassembly, the radiating diaphragms of said transducers being displacedone from another in inverse relation to the relative rise timecharacteristics of the transducers whereby the transducer having alonger rise time will be disposed closer to said area, with thediaphragm of each transducer having a longer rise time than anothertransducer closer to a point within said listening area equi-distantfrom said diaphragms than each other transducer having a shorter risetime.